find_calib_objectT_find_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject (Operator)

Name

find_calib_objectT_find_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject — Find the HALCON calibration plate and set the extracted points and contours in a calibration data model.

Signature

Description

find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject searches in ImageImageImageImageImageimage for a HALCON calibration plate corresponding to the description of the calibration object with the index CalibObjIdxCalibObjIdxCalibObjIdxCalibObjIdxCalibObjIdxcalibObjIdx from the calibration data model CalibDataIDCalibDataIDCalibDataIDCalibDataIDCalibDataIDcalibDataID. If a calibration plate is found, find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject extracts the centers and the contours of its marks and estimates the pose of the plate relative to the observing camera CameraIdxCameraIdxCameraIdxCameraIdxCameraIdxcameraIdx. All collected observation data is stored in the calibration data model for the calibration object pose CalibObjPoseIdxCalibObjPoseIdxCalibObjPoseIdxCalibObjPoseIdxCalibObjPoseIdxcalibObjPoseIdx. In order to ensure a successful detection of the calibration plate, the entire calibration plate has to be visible in the image if calibration plates with rectangularly arranged marks are used, whereas it is sufficient for calibration plates with hexagonally arranged marks if at least one of the finder pattern is completely visible.

Preparation of the input data

Before the operator find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject can be called, a calibration data model has to be defined performing the following steps:

1. Create a calibration data model with the operator create_calib_datacreate_calib_dataCreateCalibDatacreate_calib_dataCreateCalibDataCreateCalibData, specifying the number of cameras in the setup and the number of used calibration objects.

2. Specify the camera type and the initial internal camera parameters for all cameras with the operator set_calib_data_cam_paramset_calib_data_cam_paramSetCalibDataCamParamset_calib_data_cam_paramSetCalibDataCamParamSetCalibDataCamParam. Note that only cameras of the same type can be calibrated in a single setup.

3. Specify the description of all calibration objects with the operator set_calib_data_calib_objectset_calib_data_calib_objectSetCalibDataCalibObjectset_calib_data_calib_objectSetCalibDataCalibObjectSetCalibDataCalibObject. Note that for a successful call of find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject a valid description file of the calibration plate is necessary. This description file has to be set beforehand via the operator set_calib_data_calib_objectset_calib_data_calib_objectSetCalibDataCalibObjectset_calib_data_calib_objectSetCalibDataCalibObjectSetCalibDataCalibObject. As a consequence, the usage of a user-defined calibration object can only be made by the operator set_calib_data_observ_pointsset_calib_data_observ_pointsSetCalibDataObservPointsset_calib_data_observ_pointsSetCalibDataObservPointsSetCalibDataObservPoints.

Collecting observation data

find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject is used to collect observations in a calibration data model. Beyond, it stores additional observation data that cannot be added to the model with set_calib_data_observ_pointsset_calib_data_observ_pointsSetCalibDataObservPointsset_calib_data_observ_pointsSetCalibDataObservPointsSetCalibDataObservPoints and that is dependent on the used calibration plate. While for calibration plates with rectangularly arranged marks (see gen_caltabgen_caltabGenCaltabgen_caltabGenCaltabGenCaltab) the rim of the calibration plate is added to the observations, calibration plates with hexagonal pattern (see create_caltabcreate_caltabCreateCaltabcreate_caltabCreateCaltabCreateCaltab) store one of their finder pattern. Additionally and irrespective of the used calibration plate, the contour of each mark is added to the calibration model.

Setting additional parameters

Using calibration plates with hexagonally arranged marks, the following additional parameter can be set via GenParamNameGenParamNameGenParamNameGenParamNameGenParamNamegenParamName and GenParamValueGenParamValueGenParamValueGenParamValueGenParamValuegenParamValue:

'sigma'"sigma""sigma""sigma""sigma""sigma":

Smoothing factor for the extraction of the mark contours. For increasing values of 'sigma'"sigma""sigma""sigma""sigma""sigma", the filter width and thereby the amount of smoothing increases (see also edges_sub_pixedges_sub_pixEdgesSubPixedges_sub_pixEdgesSubPixEdgesSubPix for the influence of the filter width on the Canny filter).

Suggested values: 0.5, 0.7, 0.9, 1.0 (default), 1.2, 1.5

For calibration plates with rectangularly arranged marks, find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject essentially encapsulates the sequence of three operator calls: find_caltabfind_caltabFindCaltabfind_caltabFindCaltabFindCaltab, find_marks_and_posefind_marks_and_poseFindMarksAndPosefind_marks_and_poseFindMarksAndPoseFindMarksAndPose and set_calib_data_observ_pointsset_calib_data_observ_pointsSetCalibDataObservPointsset_calib_data_observ_pointsSetCalibDataObservPointsSetCalibDataObservPoints. For this kind of calibration plates the following parameters can be set using GenParamNameGenParamNameGenParamNameGenParamNameGenParamNamegenParamName and GenParamValueGenParamValueGenParamValueGenParamValueGenParamValuegenParamValue:

'alpha'"alpha""alpha""alpha""alpha""alpha":

Smoothing factor for the extraction of the mark contours. For increasing values of 'alpha'"alpha""alpha""alpha""alpha""alpha", the filter width and thereby the amount of smoothing decreases (see also edges_sub_pixedges_sub_pixEdgesSubPixedges_sub_pixEdgesSubPixEdgesSubPix for the influence of the filter width on the Lanser2 filter ).

Suggested values: 0.5, 0.7, 0.9 (default), 1.0, 1.2, 1.5

'gap_tolerance'"gap_tolerance""gap_tolerance""gap_tolerance""gap_tolerance""gap_tolerance":

Tolerance factor for gaps between the marks. If the marks appear closer to each other than expected, you might set 'gap_tolerance'"gap_tolerance""gap_tolerance""gap_tolerance""gap_tolerance""gap_tolerance" < 1.0 to avoid disturbing patterns outside the calibration plate to be associated with the calibration plate. This can typically happen if the plate is strongly tilted and positioned in front of a background that exposes mark-like patterns. If the distances between single marks vary in a wide range, e.g., if the calibration plate appears with strong perspective distortion in the image, you might set 'gap_tolerance'"gap_tolerance""gap_tolerance""gap_tolerance""gap_tolerance""gap_tolerance" > 1.0 to enforce the marks grouping (see also find_caltabfind_caltabFindCaltabfind_caltabFindCaltabFindCaltab).

Suggested values: 0.75, 0.9, 1.0 (default), 1.1, 1.2, 1.5

'max_diam_marks'"max_diam_marks""max_diam_marks""max_diam_marks""max_diam_marks""max_diam_marks":

Maximum expected diameter of the marks (needed internally by find_marks_and_posefind_marks_and_poseFindMarksAndPosefind_marks_and_poseFindMarksAndPoseFindMarksAndPose). By default, this value is estimated by the preceding internal call to find_caltabfind_caltabFindCaltabfind_caltabFindCaltabFindCaltab. However, if the estimation is erroneous for no obvious reason or the internal call to find_caltabfind_caltabFindCaltabfind_caltabFindCaltabFindCaltab fails or is simply skipped (see 'skip_find_caltab'"skip_find_caltab""skip_find_caltab""skip_find_caltab""skip_find_caltab""skip_find_caltab" below), you might have to adjust this value.

Suggested values: 50.0, 100.0, 150.0, 200.0, 300.0

'skip_find_caltab'"skip_find_caltab""skip_find_caltab""skip_find_caltab""skip_find_caltab""skip_find_caltab":

Skip the internal call to find_caltabfind_caltabFindCaltabfind_caltabFindCaltabFindCaltab. If activated, only the domain of ImageImageImageImageImageimage reduces the search area for the internal call of find_marks_and_posefind_marks_and_poseFindMarksAndPosefind_marks_and_poseFindMarksAndPoseFindMarksAndPose. Thus, a user defined calibration plate region can be incorporated by setting 'skip_find_caltab'"skip_find_caltab""skip_find_caltab""skip_find_caltab""skip_find_caltab""skip_find_caltab"='false'"false""false""false""false""false" and reducing the ImageImageImageImageImageimage domain to the user region.

List of values: 'false'"false""false""false""false""false" (default), 'true'"true""true""true""true""true"

If using a HALCON calibration plate as calibration object, it is recommended to use find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject instead of set_calib_data_observ_pointsset_calib_data_observ_pointsSetCalibDataObservPointsset_calib_data_observ_pointsSetCalibDataObservPointsSetCalibDataObservPoints where possible, since the contour information, which it stores in the calibration data model, enables a more precise calibration procedure with calibrate_camerascalibrate_camerasCalibrateCamerascalibrate_camerasCalibrateCamerasCalibrateCameras.

After a successful call to find_calib_objectfind_calib_objectFindCalibObjectfind_calib_objectFindCalibObjectFindCalibObject, the extracted points can be queried by get_calib_data_observ_pointsget_calib_data_observ_pointsGetCalibDataObservPointsget_calib_data_observ_pointsGetCalibDataObservPointsGetCalibDataObservPoints and the extracted contours can be accessed by get_calib_data_observ_contoursget_calib_data_observ_contoursGetCalibDataObservContoursget_calib_data_observ_contoursGetCalibDataObservContoursGetCalibDataObservContours.

Parallelization

• Multithreading type: reentrant (runs in parallel with non-exclusive operators).
• Multithreading scope: global (may be called from any thread).
• Automatically parallelized on internal data level.

This operator modifies the state of the following input parameter:

• CalibDataIDCalibDataIDCalibDataIDCalibDataIDCalibDataIDcalibDataID

Parameters

Possible Predecessors

read_imageread_imageReadImageread_imageReadImageReadImage, find_marks_and_posefind_marks_and_poseFindMarksAndPosefind_marks_and_poseFindMarksAndPoseFindMarksAndPose, set_calib_data_cam_paramset_calib_data_cam_paramSetCalibDataCamParamset_calib_data_cam_paramSetCalibDataCamParamSetCalibDataCamParam, set_calib_data_calib_objectset_calib_data_calib_objectSetCalibDataCalibObjectset_calib_data_calib_objectSetCalibDataCalibObjectSetCalibDataCalibObject

Possible Successors

set_calib_dataset_calib_dataSetCalibDataset_calib_dataSetCalibDataSetCalibData, calibrate_camerascalibrate_camerasCalibrateCamerascalibrate_camerasCalibrateCamerasCalibrateCameras

Alternatives

find_caltabfind_caltabFindCaltabfind_caltabFindCaltabFindCaltab, find_marks_and_posefind_marks_and_poseFindMarksAndPosefind_marks_and_poseFindMarksAndPoseFindMarksAndPose, set_calib_data_observ_pointsset_calib_data_observ_pointsSetCalibDataObservPointsset_calib_data_observ_pointsSetCalibDataObservPointsSetCalibDataObservPoints

Module

Calibration